The present invention relates to a weld stud having a cylindrical section permitting engagement by a stud welding gun, joined by a shoulder on to a threaded shank covered up to the shoulder by a cap nut made of plastics.
Known stud welding assemblies of this kind have a thread within the region of the shank of the weld stud, which is adapted for the assembly of a structural member at a later time and serves for the attaching of the can nut which, when screwed on to the weld stud, runs with its flat end face up against a flat shoulder face at the end of the thread and, as a function of the force with which the cap nut is screwed thereon, is pressed more or less firmly against the shoulder. A weld stud designed in this way may be welded to any structural member, for which a known stud welding gun can be used, which engages the weld stud in its region between the shoulder and the end face to be welded by means of gripping jaws, so that a weld stud provided with a cap nut can be held securely on the one hand while ensuring the necessary contact making with the weld stud on the other hand. In order not to obstruct the jaws of the weld gun in their gripping operation, the region of the weld stud before the shoulder has the same outside diameter as the cap nut. Weld studs designed in this way are obtainable commercially; they are also welded on in this manner in order to ensure that, for instance in a subsequent spraying operation for covering the structural member with a coat of paint, e.g. for the body of a motor vehicle, the paint cannot reach the threaded area of the weld stud, so that, if in the course of assembly a structural member is to be screwed on to the weld stud, the cap nut is unscrewed, whereupon the structural member is presented with a clean thread, free of any paint. It has however become evident that, because the cap nut is often screwed more or less tight, the tightness of the aforementioned end faces, which abut each other, is not always ensured. Sometimes, therefore, as a result of a gap remaining between the said end faces, possibly caused by vibration during transport or during the processing, paint can penetrate under the cap nut and thus contaminate the thread of the weld stud.
It is an object of the present invention to design a weld stud with a cap nut such that, with the cap nut screwed on reliable sealing of the thread is assured without imposing special demands on the force required for tightening the cap nut.